Preparation of organic derivatives of cellulose



Patented Jan. 18, 1938 PREPARATION OF ORGANIC DERIVATIVES OF CELLULOSE Herbert E. Martin and Dorsey A. Ensor, Cumberland, Md, assignors to Celanese Corporation of America, a corporation of Delaware No Drawing. Application September 30, 1936, Serial No. 103,386

9 Claims. (Cl. 260102) This invention relates to the treatment of organic derivatives of cellulose, such as the organic esters of cellulose, to remove therefrom, or to make inactive, corrosive compounds or compounds that cause the organic derivatives of cellulose to have a corrosive effect on metallic surfaces. The so treated organic derivatives of cellulose may be formed into filaments, films and molded articles without appreciably corroding the spinning jets or other metallic surfaces contacted by solutions of the organic derivative of cellulose.

An object of the invention is the economic and expeditious production of organic derivatives of cellulose that, when dissolved in a solvent, form solutions that are less corrosive than similar solutions formed of untreated organic derivatives of cellulose. Other objects of the invention Will appear from the following detailed description.

In the production of organic derivatives of cellulose there are produced various compounds that are either corrosive to metals or, when an organic derivative of cellulose is dissolved in a solvent therefor, cause the formation of compounds that are corrosive to metals. Examples of one type of such compounds are those containing sulphur. These compounds, prior to this invention, were separated from the derivative of cellulose, if at all, only by elaborate and involved treatments. By employing this invention, however, organic esters of cellulose either before, during or after being stabilized, are treated with an agent that tends to remove corrosive compounds, or compounds which tend to produce corrosive compounds. The treatment with the agent is simple and inexpensive. The treatment in accordance with this invention is carried out to such an extent as to produce an organic derivative of cellulose that is substantially non-corrosive and is completed in a short period of time.

Organic derivatives of cellulose treated in accordance with this invention may be spun into filaments by extruding the same through jets into a solidifying medium. The organic derivative of cellulose so treated does not attack the metal surrounding the orifice. When the metal of the spinning jet is attacked, the size of the orifice is enlarged or particles of the corroded metal wedged in the orifice, thus producing filaments of undesired denier. Furthermore, since organic derivatives of cellulose treated in accordance with this invention do not attack metal parts contacted thereby, they do not pick up metallic salts which tend to discolor articles formed therefrom.

In accordance with this invention, we treat precipitated or solid organic derivatives of cellulose. preferably at elevated temperatures, with a dilute solution of an organic reducing agent. After this treatment, the derivatives of cellulose may be washed substantially free of the treating compound and/or the reaction products formed by same. If desired, at least a trace of the organic reducing agent may be left in the derivative of cellulose. The organic derivatives of cellulose may be treated before or after the treatment with the organic reducing agent with chlorine or chlorine-liberating compound such as sodium hypochlorite and the like. The organic derivatives of cellulose thus treated, when dissolved in the solvent therefor, forms a solution which is substantially non-corrosive.

This invention is especially applicable to the treatment of any organic esters of cellulose such as cellulose acetate, cellulose formate, cellulose propionate and cellulose butyrate that are formed by processes which tend to produce corrosive materials. It is also applicable in an obvious way to the treatment of nitrocellulose, cellulose ethers and mixed esters and ethers of cellulose. Examples of cellulose ethers are ethyl cellulose, methyl cellulose and benzyl cellulose.

The organic esters of cellulose that lend themselves to this invention may be made by any of the methods now employed to make the same. For example, cellulose (cotton linters, cotton, wood pulp, etc.) i with or without a pretreatment in organic acid such as acetic acid and formic acid, is esterified by treating the same with an acid anhydride in the presence of an acid solvent and a catalyst. In place of the acid solvent or in connection therewith there may be used suspension liquids such as benzol. The acid solvent may be a concentrated acid corresponding to the anhydride employed or it may be, as is preferred glacial acetic acid. Examples of catalysts are sulphuric acid, phosphorous acid, hydrochloric acid, zinc chloride and mixtures of these.

After esterification, sufficient water may be added to convert any remaining anhydride to the corresponding acid and the mixture hydrolized or ripened until the desired solubility characteristics are developed. The catalyst is then neutralized and water or other non-solvent for the ester added to precipitate the ester. During this precipitation step the ester may, if desired, be treated with a solution of a hypochlorite or other chlorineliberating compound to bleach the same. The ester is then separated and washed free of the acid solution. The cellulose ester may then be stabilized by treating with boiling water containing small amounts of mineral acid or with steam with or without pressure. Although stabilized, the ester may contain compounds which, when the ester is in solution, cause the solution to corrode or attack metals.

We have found that, if the ester is treated after precipitation, but prior to stabilizing, by soaking the ester in a dilute aqueous solution of an organic reducing agent, the resulting ester is substantially free of the compounds, the exact chemical structure of which is unknown, that cause the ester or solution thereof to have a corrosive effect on metals. We have also found that these undesirable compounds may be removed or diminished to.

below an effective quantity by soaking the stabilized ester in a dilute solution of an organic reducing .agent. The latter method of treating stabilized esters is preferable. It is in general more effective and has less tendency to alter the viscosity and solubility characteristics of the ester. The soaking treatment is preferably carried on at elevated temperatures, for instance, at from 50 to 100 C. Other methods than soaking may be employed to treat the organic derivatives of cellulose with a dilute solution of the organic reducing agent, such as spraying the solution on to the organic derivative of cellulose or working the organic derivative in a counter-current manner in a stream of said dilute solution.

The treating liquid or bath may be formed by dissolving any suitable organic reducing agent in an aqueous medium. The organic reducing agent may be, for example, sodium sulphoxylate formaldehyde, zinc sulphoxylate formaldehyde and equivalent organic reducing compounds. When treating organic esters of cellulose, the percentage of organic reducing agent in the treating bath should be relatively small. The amount of the aqueous solution of the organic reducing agent is preferably from 4 to 20 times or more the weight of the derivative of cellulose, the concentration of the aqueous solution being such that the amount of organic reducing agent present in the bath is between 0.03 to 1% on the weight of the derivative of cellulose employed and preferably from 0.1 to 0.5%. Although the treating bath may be of any suitable temperature, for instance from 50 to 100 C., it has been found preferable to maintain the temperature at from C. to the boiling point of the bath.

To further describe the invention and not as a limitation, the following examples are given:

Example I Precipitated stabilized cellulose acetate, after being washed to neutral state, is boiled for 4 hours in an aqueous bath containing about 0.394% of sodium sulphoxylate formaldehyde on the weight of the cellulose acetate. The bath is approximately 18 times the weight of the cellulose acetate. The cellulose acetate is then washed substantially free of the treating liquid, dried and dissolved in a suitable solvent. The resulting solu* tion is found to be substantially free of any corrosive compounds.

Example II Precipitated unstabilized cellulose acetate, after being washed to neutral state, is boiled for 4 hours in an aqueous bath containing about 0.394% of sodium sulpho-xylate formaldehyde on the weight of the cellulose acetate. The cellulose acetate is then washed substantially free of the treating liquid, stabilized in a normal manner, dried and dissolved in a suitable solvent.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by Letters Patent is:

1. Method of reducing the corrosive properties of a derivative of cellulose, which comprises treating the derivative of cellulose in a solid, finely divided condition with a reducing agent, selected from the group consisting of sodium sulphoxylate formaldehyde and zinc sulphoxylate formaldehyde, in a quantity sufficient to remove the corrosive compounds.

2. Method of reducing the corrosive properties of an organic acidv ester of cellulose, which comprises treating the organic acid ester of cellulose in a solid, finely divided condition with a reducing agent, selected from the group consisting of sodium sulphoxylate formaldehyde and zinc sulphoxylate formaldehyde, in a quantity suificient to remove the corrosive compounds.

3. Method, of reducing the corrosive properties of cellulose acetate, which comprises treating the cellulose acetate in a solid, finely divided condition with a reducing agent, selected from the group consisting of sodium sulphoxylate formaldehyde and zinc sulphoxylate formaldehyde, in a quantity suflicient to remove the corrosive compounds.

4. Method of reducing the corrosive properties of an organic acid ester of cellulose, which comprises treating the organic acid ester of cellulose in a solid, finely divided condition with a dilute aqueous solution of a reducing agent, selected from the group consisting of sodium sulphoxylate formaldehyde and zinc sulphoxylate formaldehyde, in a quantity sufficient to remove the corrosive compounds.

5. Method of reducing the corrosive properties of cellulose acetate, which comprises treating the cellulose acetate in a solid, finely divided condition with a dilute aqueous solution of a reducing agent, selected from the group consisting of sodium sulphoXyla-te formaldehyde and zinc sulphoxylate formaldehyde, in a quantity sufiicient to remove the corrosive compounds.

6. Method of reducing the corrosive properties of an organic acid ester of cellulose, which comprises treating a stabilized organic acid ester of cellulose in a solid, finely divided condition with a reducing agent, selected from the group consisting of sodium sulphoxylate formaldehyde and zinc v sulphoxylate formaldehyde, in a quantity sufficient to remove the corrosive compounds.

7. Method of reducing the corrosive properties of cellulose acetate, which comprises treating a stabilized cellulose acetate in a solid, finely divided condition with a reducing agent, selected from the group consisting of sodium sulphoxylate formaldehyde and zinc sulphoxylate formaldehyde, in a quantity sufficient to remove the corrosive compounds.

8. Method of reducing the corrosive properties of an organic acid ester of cellulose, which comprises treating the organic acid ester of cellulose in a solid, finely divided condition with an aqueous solution containing from .03 to 1% on the Weight of the organic acid ester of cellulose of sodium sulph'oxylate formaldehyde.

9. Method of reducing the corrosive properties of cellulose acetate, which comprises treating the cellulose acetate in a solid, finely divided condition with an aqueous solution containing from .03 to 1% on the weight of the cellulose acetate of sodium sulphoxylate formaldehyde.

HERBERT E. MARTIN.

DORSEY A. ENSOR. 

